Generation of a More Immunogenic Measles Vaccine by Increasing Its Hemagglutinin Expression

Abstract

Imported measles virus (MV) outbreaks are maintained by poor vaccine responders and unvaccinated people. A convenient but more immunogenic vaccination strategy would enhance vaccine performance, contributing to measles eradication efforts. We report here the generation of alternative pediatric vaccines against MV with increased expression of the H protein in the background of the current MV vaccine strain. We generated two recombinants: MVvac2-H2, with increased full-length H expression resulting in a 3-fold increase in H incorporation into virions, and MVvac2-Hsol, vectoring a truncated, soluble form of the H protein that is secreted into the supernatants of infected cells. Replication fitness was conserved despite the duplication of the H cistron for both vectors. The modification to the envelope of MVvac2-H2 conferred upon this virus a measurable level of resistance to in vitro neutralization by MV polyclonal immune sera without altering its thermostability. Most interestingly, both recombinant MVs with enhanced H expression were significantly more immunogenic than their parental strain in outbred mice, while MVvac2-H2 additionally proved more immunogenic after a single, human-range dose in genetically modified MV-susceptible mice. IMPORTANCEMeasles incidence was reduced drastically following the introduction of attenuated vaccines, but progress toward the eradication of this virus has stalled, and MV still threatens unvaccinated populations. Due to the contributions of primary vaccine failures and too-young-to-be-vaccinated infants to this problem, more immunogenic measles vaccines are highly desirable. We generated two experimental MV vaccines based on a current vaccine's genome but with enriched production of the H protein, the main MV antigen in provoking immunity. One vaccine incorporated H at higher rates in the viral envelope, and the other secreted a soluble H protein from infected cells. The increased expression of H by these vectors improved neutralizing responses induced in two small-animal models of MV immunogenicity. The enhanced immunogenicity of these vectors, mainly from the MV that incorporates additional H, suggests their value as potential alternative pediatric MV vaccines. Despite the existence of an effective vaccine, measles virus (MV) infections remain an insidious threat to global health. After decades of reduction in measles-related mortality due to vaccination, this has stalled at between 110,000 and 120,000 deaths/year since 2012. Approximately 20 million people are infected by measles each year, with significant morbidity and up to 1% mortality (1). In 2014, the United States saw the highest number of annual measles cases since native transmission was declared locally eliminated in 2000 (2) and experienced a large multistate outbreak in the first months of 2015 (3).Protecting young infants against measles is an important goal to attain to improve the current MV vaccine (4). The highest fatality rates due to MV infection occur in infants Ͻ1 year of age (5). Ironically, incre...

Improved Prefusion Stability, Optimized Codon Usage, and Augmented Virion Packaging Enhance the Immunogenicity of Respiratory Syncytial Virus Fusion Protein in a Vectored-Vaccine Candidate

“…In addition, we also evaluated the immunogenicity of a secreted soluble pre-F trimer. Antigens presented in the form of virus-like particles (VLPs) or in oligomerized or aggregated forms typically are more immunogenic than monomeric and nonaggregated forms (50)(51)(52)(53). In a previous study (14), we compared two versions of RSV F that had been designed to lack the TM and CT domains, which would favor secretion.…”

A Recombinant Measles Vaccine with Enhanced Resistance to Passive Immunity

“…Previously, a modified MV with increased expression and incorporation of the full-length H protein, termed MVvac2-H2, proved significantly more immunogenic than the parental vaccine MVvac2 in mature (six- to eight-week-old) outbred, non-susceptible CD1 mice and in mature genetically modified MV-susceptible HuCD46Ge-IFNar KO mice, which express the human CD46 receptor for MV vaccine strains with human-like distribution in a type I interferon knockout background. In both murine hosts, MVvac2-H2 elicited approximately 2.5-fold higher neutralization titers than MVvac2 elicited [ 15 ].…”

“…Vero/hSLAM cells served as hosts for growth of viral stocks and for neutralization assays. Methods related to the growth of cells and amplification of recombinant viruses have been detailed elsewhere [ 15 ]. MVvac2 [ 18 ] has identical amino acid coding capacity to the Moraten and Schwarz vaccine strains and so serves as a current vaccine-equivalent control.…”

“…Humoral immunity against measles was assessed by incubating two-fold dilutions of serum with 100 TCID 50 of virus on Vero/hSLAM cells in a 96-well plate format, as described previously [ 15 , 18 ]. Neutralization titer was determined as the highest dilution of sera affording elimination of infectivity, defined as the absence of syncytia.…”

“…Previously, with the goal of developing a more effective measles vaccine for young infants, we developed two recombinant modified MVs in a Moraten-equivalent background with added copies of the full-length (MVvac2-H2) or truncated (MVvac2-Hsol) hemagglutinin (H) cistron. Despite this genetic alteration, both recombinants showed a comparable in vitro replication profile as the parental, Moraten-equivalent strain in two cell lines approved for measles vaccine manufacture [ 15 ]. Based upon the results of clinical trials that demonstrated the ability of high titer doses of MV vaccine to overcome maternal antibody interference and induce immunity in young infants [ 16 ], but that subsequently demonstrated increased mortality attributed to wild type MV-like immunosuppression in high titer vaccine recipients [ 17 ], we hypothesized that our modified MVs with higher relevant H antigen expression might similarly overcome maternal immunity within a safe standard titer dose.…”